JPH04502965A - capacitive humidity sensor - Google Patents

Abstract

PCT No. PCT/NL89/00100 Sec. 371 Date Aug. 22, 1991 Sec. 102(e) Date Aug. 22, 1991 PCT Filed Dec. 28, 1989 PCT Pub. No. WO90/07708 PCT Pub. Date Jul. 12, 1990.Capacitive humidity sensor comprising a substrate, a moisture-impermeable conducting bottom layer as first capacitor plate, a dielectric layer, and a moisture-permeable conducting top layer as second capacitor plate, and connecting wires associated with the first and second capacitor plates, whereby the change in the dielectric constant, and therefore in the capacitance value, due to absorption of water molecules is measured. The substrate is a flexible copper laminate in which at least the conducting bottom layer is etched, and the conducting top layer comprises a solid printed layer having a conducting grid pattern, which is printed with conducting ink.

Description

[Detailed description of the invention] capacitive humidity sensor The present invention includes a base layer, a moisture-impermeable and conductive bottom layer as a first capacitive plate, a dielectric layer and a moisture permeable and electrically conductive top layer as a second capacitive plate; Connect the wires in combination with the first and second capacitive plates and absorb the water molecules of the dielectric material. The change in dielectric constant and therefore the capacitance value due to the change in capacitance is measured. Humidity sensor Ther is disclosed, for example, in US Patent Application No. 4,532,016.

In such sensors, which are essentially capacitive, the humidity is Measurement of the change in the dielectric constant of the dielectric medium due to the absorption of water molecules and hence the change in the capacitance value. determined by the For example, the dielectric constant of the material of the dry dielectric layer is 3.5, and the dielectric constant of the material of the dry dielectric layer is 3.5. If it is about 80, it is clear that the change in capacitance value due to moisture absorption is difficult to recognize. It will be clear. In order for the dielectric layer to absorb moisture or water, the top layer must be permeable to moisture. I have to come.

This known sensor has a glass base layer on which a tantalum as a first capacitive plate is placed. A tar board is placed. The tantalum plate is anodized so that tantalum oxide is more A thin insulating layer is obtained. The insulating layer is clearly dielectric at high relative humidity. Prevents resistive losses across the medium or shorts between plates regardless of the structure of the dielectric medium. To prevent. The generation of direct currents resulting in polarization drift as a result of electrolysis is also prevented. . The aforementioned dielectric layer is sufficiently porous to absorb moisture. The moisture-permeable top layer is e.g. For example, it is composed of porous gold or cracked chrome. Chrome is When deposited on a dielectric layer, it actually has a high tensile strength, resulting in chromium and dielectric Small cracks are created in the electric body. However, the disadvantage is that especially at the beginning of the useful life As a result, the capacitance value decreases with time. It also changes. Post-processing is required to counter this.

The manufacture of the sensor is also fraught with problems. In particular, the dimensions of the thin glass substrates that can be processed are limited, resulting in limited production rates and increased costs.

Technology has become more complex, the finished sensors are extremely delicate, and manufacturing yields have increased. is relatively low. Porous gold is affected by industrial contaminants and chrome cracks. Cracking treatment depends on fortuitous events. For finished sensors, measurement precision Another problem is that there is no separate provision for adjusting the degree.

This group of sensors can absorb the relatively high price of sensors and also – High-cost, adjustable and calibrated electronics to give wide tolerances to accuracy. suitable for the device.

The aim of the invention is to eliminate the above-mentioned problems and to provide a more durable and compatible product. Provides an inexpensive sensor that can be easily calibrated after fabrication to allow for interchangeability That's true.

According to the invention, a flexible copper laminate in which the base layer is etched with at least a conductive bottom layer as described above. solid phase printing in which the conductive top layer has a conductive lattice pattern; With a capacitive humidity sensor of the above-mentioned type, breathable with a layer, the above-mentioned objectives can be achieved. achieved.

In this embodiment according to the invention, a particularly inexpensive sensor for the consumer market is obtained, which is also suitable for industrial use. This sensor according to the invention Easy to calibrate under both humid and atmospheric conditions.

The invention will be explained in more detail on the basis of exemplary embodiments with reference to the drawings. figure In terms of FIG. 1 shows a perspective view of the layered structure of an embodiment of a sensor according to the invention. and, FIG. 2 shows a plan view of the top plate acting as the second capacitive plate of the embodiment of FIG. vinegar.

As stated above, it is an object of the present invention to provide an inexpensive sensor for consumer use.

According to the invention, the glass substrate material, which is itself an excellent material, can be used for example in printed circuit boards. It effectively replaces the copper laminates often used in (P　CB). another In this embodiment, the copper laminate is constructed of polysiloxane glass fabric or cloth. can be achieved. The moisture-impermeable bottom layer is followed by a second thin contact plate that is moisture-permeable. If needed to act as a contact plate for the top layer of the It can be etched onto the copper surface of the laminate. At a later stage of production, the bottom layer and the contact layer A connecting wire is attached to the

The use of such thin and flexible PCB laminates is important as the use is made in PCB manufacturing technology. The results obtained are also much better than those produced from thin glass substrates. Producing durable sensors. Also, for example, 50X50=2500 cells It is also possible to start with a large base layer where a sensor can be obtained. insulation polymer Under certain conditions, where the It is possible to treat two substrates at the same time back-to-back, so that one treatment It is possible to make 5000 sensors in one process.

FIG. 1 diagrammatically shows the structure of a sensor according to the invention.

1 shows a base layer consisting of a thin PCB copper laminate onto which two copper layers 2 and 3 are etched. It will be done. Layer 2 shown on the left is a moisture-impermeable layer that acts as a first capacitive plate; Layer 3 is contacted at a later manufacturing stage with a moisture permeable top layer 4 which acts as a second capacitive plate. It is a contact plate that can be touched. In the final stage, the substrate is cut into individual sensors. Once separated, connecting wires 5 are attached to layers 2 and 3.

6 shows a polymer coating that acts as an insulating layer, which is extremely thin but contains active copper. Protecting the surface of the capacitive plate 2 against erosion and contamination. Layer 6 is itself non-permeable Since it is related to the structure of the dielectric medium (, any capacitance between the described It also prevents short circuits and the flow of direct current that would cause polarization drift as a result of electrolysis. will be stopped. This layer is removed as a result of the creation of so-called "pinholes" in the active dielectric 7. This will prevent failures from occurring. The polymer 6 extends above the thin copper contact layer 3. Not yet. In the latter case, use an inert, unreactive, pinhole-free blocking polymer. It is preferable to use

The dielectric layer 7 is made of an active polymer that can be made into fibers and can be made by means of screen printing or can be deposited in other ways and thus in sufficient quantities for the operation of the humidity sensor. A very thin layer containing pores is created. In this way, the capacitance value under the influence of humidity The result is a dielectric "sponge" that changes reliably and rapidly. Therefore, a large "inhalation" and "discharge" aspects are achieved. The figure shows that layer 7 is well above contact layer 3. Indicates that it is not extended. However, other manufacturing methods are also conceivable.

4 indicates a moisture permeable top layer as a second capacitive plate extending over the whole.

A portion of the top layer extending above the dielectric layer 7 is coated with conductive ink. It has a grid shape printed on it.

The plan view shown in Figure 2 shows a mostly rectangular grid pattern, although other patterns are possible. A turned plate 7 is shown. The openings in the grate ensure the movement of moisture. Shape of grid 10 The status is important. (Conductive) Maximize the ink surface area to obtain the maximum capacitance value. However, unless the water transfer area is large enough, absorption and expulsion may take a long time. will. For example, a relatively large sensor area such as 10m+a” can give good results. In this case, the response time is adversely affected within a certain range.

11 indicates a solidly printed shape, that is, a part of the top plate with no openings; This is for contacting the contact layer 3 on the base layer 1.

12 shows a row of small electrically conductive printed areas arranged in an insulated manner. of the capacitor During construction, said rows of sub-regions 12 are placed only above the blocking polymer and the active It is avoided to be placed above the polymer. The electrostatic charge formed by this The value of capacitance is a minimum or zero.

In manufacturing, under both dry and wet conditions (delta = 0% to 100% relative Humidity range), the capacitance value of the sensor is designed to be slightly below the normal tolerance. It will be done. For automatic calibration, in a dry reference environment, the required constant (dry) reference To obtain the capacitance value, some of the small areas 12 are removed by means of small pads of conductive ink. is connected to the main grid.

13 shows another row of small conductive printed areas arranged insulated.

However, in capacitor construction these are placed above the active polymer. It will be done. These small areas also adjust the required delta capacitance value in a humid reference environment connected to the main lattice in order to

In the above, it was assumed that it is easier to add rather than reduce the capacitance value. . However, such reduction can also be accomplished by laser trimming.

After trimming, the conductive ink tracks are cured. Advantages of this "printing" method In that it can determine the exact printing shape and does not rely on accidental phenomena. be. Trimming can be done on both constant or delta values. too If processing errors occur during printing, these can be "erased" and The more expensive parts are simply coated with a blocking polymer.

Cropped small regions are shown as small squares. These are also fewer in number And it will be clear that for example two surface areas can be provided one after the other.

During manufacturing, depending on the required application, larger dimensions and, as a result, longer segments are produced. manufacturing sensors with improved response speed by obtaining Can be done. Since the contact surface occupies a significant portion of the edge surface, a more elongated design Relative to area, this would make it possible to reduce the large active surface.

Since barrier polymers are expensive, copper laminates are preferably coated on only one side. stomach. This is best done by placing two substrates back to back and treating them at the same time. It can be achieved. To do this, mask the contact layer or polish the resulting barrier layer. It is necessary. The laminate can be treated on both sides, so it is not covered with a barrier layer and therefore has no capacitance. Provide both contact layers on the other side that can be easily soldered, and attach these to the through-hole plating method. connection by means of steps or specially designed "knifetsu" contact terminals; is possible.

All non-active surfaces that are not coated with a blocking polymer are protected by the usual protection method for PCB laminates. It can be coated with a solder resist by a method.

An inexpensive humidity sensor manufactured in a reproducible manner and identified on the vine is used in the automotive industry. Window defogging systems, air handling systems for brake (shoe) systems, etc. many types of combustion engines, such as internal combustion engines, whose combustion processes are sensitive to relative humidity. Can be used for various purposes.

Copy and translation of amended sound) Submission (Article 184-8 of the Patent Law) June 27, 1991

Claims (10)

[Claims] 1. a base layer, a moisture-impermeable and conductive bottom layer as a first capacitive plate, a dielectric layer, and and a moisture-permeable and conductive top layer as a second capacitive plate; and a second capacitance plate to connect the wires and increase the dielectric constant due to absorption of water molecules. A capacitive humidity sensor in which the change in capacitance value is measured and therefore the change in capacitance value is The layers are flexible copper laminates etched with at least the aforementioned conductive bottom layer, and further wherein said conductive top layer comprises a solid printed layer having a conductive grid pattern; A capacitive humidity sensor featuring: 2. characterized in that the aforementioned top layer grid pattern is printed with conductive ink; A capacitive humidity sensor according to claim 1. 3. Contact layers in contact with the aforementioned bottom layer and the moisture permeable top layer are longitudinally connected to each other on the base layer. a parallel, moisture-impermeable insulating layer between at least said bottom layer and the dielectric layer; Furthermore, the aforementioned top layer extends both above the dielectric layer and above the contact layer, and the insulating layer extends both above the dielectric layer and above the contact layer. Inert, non-porous insulating polymer with extremely thin dielectric layer with suitable porosity a dielectric polymer deposited to create a layer, further said top layer being a suitable A conductive ink surface is used to obtain a high capacitance value and to enable absorption and ejection in a short time. The claim is characterized in that it has a lattice shape such that the area of the moisture permeable surface matches the area of the moisture permeable surface. Capacitance type humidity sensor with required range 1. 4. Capacitor according to claim 3, characterized in that the contact layer is etched into the copper laminate. Quantitative humidity sensor. 5. Claims characterized in that the copper laminate is composed of a polysiloxane woven material. Capacitive humidity sensor according to enclosure 3. 6. Electrostatic according to claim 3, characterized in that the insulating polymer is a blocking polymer. Capacitive humidity sensor. 7. The top layer has a row of small ink areas on at least one side of the grid pattern. A capacitive humidity sensor according to claim 3, characterized in that: 8. Below the rows of small ink areas (12) no dielectric polymer is placed and an insulating point is placed. There is a reamer and therefore, during pre-calibration of capacitance values in a dry atmosphere, it is necessary to The finish sensor can be used to connect small areas of ink into a grid pattern. According to claim 7, characterized in that a row of small ink areas (12) is provided. Capacitive temperature sensor. 9. Below the rows of small ink areas (13) a dielectric polymer is placed and an insulating poly Therefore, during pre-calibration of capacitance values in a humid atmosphere, there is no need to The small ink area of the finish sensor allows you to connect small areas of ink into a grid pattern. A still according to claim 7, characterized in that a row of small ink areas (13) is provided. Capacitive humidity sensor. 10. The grating pattern is adjusted by laser irradiation during pre-calibration of capacitance values. A capacitive humidity sensor according to claim 3, characterized in that: